In industrial use of torque delivering power tools such as power wrenches and nutrunners that are used for tightening joints it is important to monitor the applied torque in order to verify that the joints are fastened to a satisfactory degree. It is often desired to install a predetermined clamp force into a joint. Normally it is however difficult to monitor the clamp force and it is therefore common practice to instead control a tightening so as to install a specific target torque in a joint.
A difficulty related to the monitoring of a delivered torque is that there are losses due to friction in the joint and due to gear ripple and the like inside the tool that affects the accuracy of the monitoring values in an unpredictable manner. The friction in a joint may vary largely between different joints, but it may be presumed to be constant for a specific joint at specific conditions, and there are manners of estimating the friction for a specific joint, both by empiric testing or by real time monitoring during the tightening of a joint.
The variations that are due to gear ripple and the like inside the tool are more difficult to predict. One way of eliminating these problems is to locate a torque meter as close to the joint as possible, i.e. on the output shaft. There is however a conflicting desire to minimize the size of the power tool in general and specifically to minimize the number of delicate components in the vicinity of the output shaft.
Hence, there is a need of a torque delivering power tool which is adapted to deliver a precise output torque but which does not involve a lot of delicate components in the vicinity of the output shaft.